Various types of positioning systems are known in the art. For example, satellite navigation systems provide autonomous geospatial positioning with global coverage. A global navigation satellite system (GNSS) allows GNSS receivers to determine their location on the earth using signals transmitted from satellites, including longitude, latitude and altitude, to within a few meters or even centimeters.
For example, orbiting satellites broadcast their precise orbital data containing the position of the satellite and the precise time when the signal was transmitted. The position of the satellite may be transmitted in a data message that is superimposed on a code that serves as a timing reference. The receiver can then compare the time of broadcast encoded in the transmission with the time of reception measured by an internal clock, thereby measuring the time of flight to the satellite. Several such measurements can be made at the same time to different satellites, allowing a precise determination of the position of the receiver.
Each individual distance measurement made by the receiver traces the receiver on the surface of a spherical shell at the measured distance from the satellite. By taking several such measurements and determining an intersecting point of the spherical shells, a position fix can be generated. Generally, with the latitude, longitude, altitude and time unknown, i.e. four unknown parameters, signals from four satellites are needed for a precise position determination.
A common and well known application of such global positioning systems is to use a satellite navigation system receiver to determine the position of a vehicle, a person, etc.
Moreover, it is known to use satellite navigation system receivers in measuring very slow motion, for example tectonic drift, to track the slow movement or deformation of continents. By deploying a network of satellite navigation system receivers, maps of the tectonic changes of the earth surface can be generated.
However, certain events may disturb the slow drift that is tracked by the satellite navigation system receivers, and it is required to assess such disturbances. For example, earthquakes or landslides may cause large movements or deformations of the earth surface over a very short period of time as compared to the slow tectonic drifts.
In order to comprehensively monitor slow earth deformation or other types of slow movements with sudden rapid changes, a system capable of handling both types of motion is required, e.g. a slow tectonic drift and sudden movements caused by earthquakes, landslides, etc.
In the absence of rapid motion a variety of filter techniques to obtain sufficient accuracy is known, but to also track rapid motion a filter is needed with a sufficient dynamic range such as the known real time kinematic (RTK) filter. One problem with known RTK solutions is, however, that high accuracies can only be obtained when carrier phase ambiguities can be resolved. Carrier phase ambiguities result from the fact that a position determination in an RTK filter based system uses a phase of a carrier wave. However, the phase of a wave is ambiguous as the same phase reoccurs with each oscillation of the carrier signal. In RTK filter solutions carrier phase ambiguities restrict position tracking systems to networks with a satellite navigation receiver spacing below e.g. 100 kilometers. Moreover, with RTK filters solutions problems occur with multipath propagation.